Iron-based amorphous metal alloys and amorphous/microcrystalline metal alloys such as Fe--P--C, Fe--Si--B, Fe--Zr, Fe--Zr--B, and Fe--Cu--Nb--Si--B are well known in the art. To obtain the amorphous state, a molten alloy of a suitable composition is quenched rapidly, or a deposition technique is used. An amorphous state is distinguished from a crystalline state by the absence of an ordered atomic arrangement. In general, the amorphous state will convert upon heating to a crystalline state with initial crystals nucleated having a fine structure of a bcc (body-centered cubic) Fe solid solution, and upon further heating to a sufficiently high temperature, the entire system will crystallize.
Nanocrystalline materials and methods for producing them from iron-based amorphous metals with boron metalloid chemistry are exemplified by U.S. Pat. Nos. 5,474,624 and 5,449,419 to K. Suzuki, et al.; U.S. Pat. Nos. 5,160,379, 5,069,731 and 4,985,089 to Y. Yoshizawa, et al.; and by Yoshizawa et al. (J Appl. Phys. 64(10), Nov. 15, 1988). Soft magnetic properties were reported by adding copper and niobium to iron-silicon-boron alloys. Such material currently has the name FINEMET.RTM. and reportedly has an ultrafine grain structure composed of bcc Fe solid solution. Desirable properties of FINEMET.RTM. are attributed to the bcc solid phase which contains boron and silicon. The general starting ingredients for producing such material, for example, technical ferroboron, niobium or ferroniobium, zirconium and copper are refined or semi-refined products and are quite expensive. In some cases, copper and niobium are added to the starting melts prior to quenching to an amorphous state at levels of 0.2-4.0 atomic percent each. Copper and niobium will form a molecular cluster that aids in the nucleation and control of the size of ferrite iron crystals, however, these materials, especially niobium, are very expensive and are a major drawback to further commercialization of these boron-stabilized nanocrystalline materials.
Typically, amorphous metal alloys are produced by the very rapid cooling of a liquid metal alloy at approximately 10.sup.6 .degree.C./second. The rapid cooling rate is required for the maintenance of the non-crystalline structure of the liquid alloy when it solidifies. Numerous methods are known for achieving this rapid cooling. One such technique employs rapid cooling at a moving cooled surface, such as a wheel or belt to produce thin wire strands, ribbons or other thin shapes. The thin structure may be laminated or wound to form a magnetic core, for example.
Allied Signal's METGLAS.RTM. amorphous metal alloy is an industry standard having a thickness of from 20-23 microns. U.S. Res. Pat. No. 32,925 to Chen et al. relates to amorphous metals and amorphous metal articles having up to one-quarter of the metal replaced by elements such as Mo, W, and Cu, and where wires, for example, may be rendered partially crystalline because the quenching rate is lower than that required to obtain the totally amorphous state for the composition quenched. This material has an amorphous outer surface and a more crystalline inner area and is not amorphous or microcrystalline throughout.
A follow-up heat treatment is often used to relieve internal stresses in the material and should be performed at a temperature that does not result in significant overheating of the alloy. Otherwise, upon heating, the tendency of metals to crystallize will result in the loss of the amorphous structure of the alloy.
Inoue and Gook (Materials Transactions, JIM, 37(1), 32-38, 1996) relate to Fe-based glassy alloys having a wide supercooled liquid region before crystallization. Inoue et al. (Materials Transations, JIM, 36(12) 1427-1433, 1995) relate to bulk Fe-based glassy alloys prepared by copper mold casting in cylindrical form with diameters of 0.5 and 1.0 mm. Such materials lack the low coercivity and high permeability of compositions of the present invention.
Fujii et al. (J.AppL. Phys. 70(10), Nov. 15, 1991) relates to magnetic properties of fine crystalline Fe--P--C--Cu--X alloys. Copper is cited as the essential element for the precipitation of the bcc Fe phase in Fe--P--C as well as Fe--Si--B amorphous alloys. Further, the P concentration is cited as controlling the structure and soft magnetic properties.
U.S. Pat. Nos. 5,518,518 and 5,547,487 relate to the production of amorphous metal alloys from impure by-products of the electric furnace process for manufacturing elemental phosphorus. The by-product FERROPHOS.RTM. iron phosphide, sold by FMC Corporation, was employed as a source of iron, phosphorus, chromium, and vanadium while additional iron was included for desired electromagnetic properties of the alloy. In spite of the additional iron, however, a magnetic saturation induction of only 9000 gauss or 0.9 tesla, and an ultimate tensile strength of 1250 Mpa were obtained. These values are insufficient for alloys suitable for use in electrical appliances such as transformer cores, motors, or other devices that require excellent ferromagnetic properties.
No practical guideline is known for predicting with certainty which of the multitude of different possible alloys will yield an amorphous metal alloy or amorphous/microcrystalline metal alloy having desired ferromagnetic properties.
The present invention provides amorphous metal alloys and amorphous/microcrystalline metal alloys having improved magnetic properties. The improved properties are a function of the particular elements and ratios of elements used in the amorphous metal alloys and careful attention to the time and temperature of heating an amorphous metal alloy to form an amorphous/microcrystalline alloy.